The present invention relates generally to telemetry transmitters, and more specifically the invention pertains to a system which measures the steady state phase deviation of a biphase modulated telemetry transmitter, the modulation source being a pulse coded modulation (PCM) bit stream.
In phase modulation, the term "phase deviation" refers to the peak difference of the relative phase angle of the sine wave carrier do to the modulating signal as expressed in radians or degrees. The task of measuring the steady state phase deviation in a phase modulated telemetry transmitter is accomplished, to some extent, by the systems disclosed in the following U.S. Patents, the disclosure of which are incorporated herein by reference:
U.S. Pat. No. 4,354,278 issued to Clark et al;
U.S. Pat. No. 4,635,260 issued to Sestan;
U.S. Pat. No. 4,763,317 issued to Lehman et al; and
U.S. Pat. No. 4,833,466 issued to Lowenson et al.
The method commonly used to determine phase deviation involves measuring a carrier null on a spectrum analyzer. But that method is only accurate if a square wave is used as the modulating signal. In some test situations for telemetry transmitters, an indeterminate bit stream is the only source available to modulate the carrier signal, and a need remains to provide a new method of determining phase deviation. The present invention is intended to satisfy that need.